The present invention relates to a magnetogenerator and, particularly, to a contactless multi-pole magnetogenerator.
FIG. 7 shows an example of a conventional magnetogenerator which comprises a fly-wheel 1 in the form of a bowl which rotates in synchronism with an engine rotation and a plurality (12) of permanent magnets 2 having a common length arranged along an inner peripheral surface of the fly-wheel 1 with magnetic poles of the magnets being arranged radially alternatively. A stator 3 is arranged in a space within the fly-wheel 1.
The stator 3 comprises a magnetic core 4 in the form of a ring formed on an outer periphry thereof with a plurality (16) of radially outwardly protruding poles 4a on each of which a coil is wound to form a generating coil. One of the generating coils 5 is a relatively large cold for ignition purpose and the other 6 are for additional power generation. The power generating coil 5 is used to generate a power to be utilized by an engine ignition circuit to ignite an engine and the additional power generating coils 6 are used to generate a power for car accessories other than lamps etc. of a car.
A trigger pole 7 of an angle position detector is provided on an outer periphery of the fly-wheel 1, which produces in a signal coil a reference signal having a polarity which alternates at times when leading and trailing edges of the trigger pole 7 pass over an electrode 8a of an electromagnetic pick-up device 8. Portions of the reference signal having opposite polarities are used as a first angle signal a corresponding to a predetermined crank position of the engine and a second angle signal b corresponding to a crank position which is delayed by a predetermined angle from the position at which the first angle signal a is produced, respectively. The position or length of the trigger pole 7 with respect to the fly-wheel 1 is determined such that these reference signal portions a and b are produced within a negative half period of an output produced by the ignition power generating coil 5.
The operation of the magnetogenerator mentioned above will be described with reference to a circuit diagram shown in FIG. 8 and signal waveforms shown in FIG. 9. FIG. 8 is a circuit diagram of a usual capacitor discharge type ignition device (CDI) in which reference numeral 9 depicts a power source for a lead angle circuit, 10 is a mask means, 11 is a diode for rectifying an alternating output of the ignition power generating coil 5 and charging an ignition capacitor 12, and 13 is a thyristor which is a switching element for supplying charge of the capacitor 12 upon a signal from a signal source to be described to a primary coil 14a of an ignition coil 14 to discharge a high voltage induced in a secondary coil 14b thereby at an ignition plug 15 to thereby ignite the engine.
Reference numeral 8b depicts the signal coil of the electromagnetic pick-up device 8, 16 is a first RC bias circuit constituted with a capacitor 16a and a resistor 16b, 17 is a second RC bias circuit constituted with a capacitor 17a and a resistor 17b, and 18 is a lead angle circuit for controlling an igntion timing of the engine.
The alternating output prodecued by the ignition power generating coil 5 is rectified by the diode 11 and charges the capacitor 12. Simultaneously, it is also rectified by the diode 9a of the power source 9 for the lead angle circuit, is limited in current by the resistor 9b, and charges the capacitor 9c. Charge of the capacitor 9c is used as a power source for the lead angle circuit 18.
On the other hand, one portion of the output of the signal coil 8b of one polarity is rectified by the diode 19 and supplied through the first RC bias circuit 16 to a gate of the semiconductor switching element 13 as the second angle signal b, and the other signal portion of the other polarity is rectified by a diode 20 and supplied through the second RC bias circuit 17 to the lead angle circuit 18 as the first angle signal a. The lead angle circuit 18 operates the ignition timing on the first angle signal, which is supplied to the gate of the semiconductor switching element 13. In this case, since the switching element 13 is turned on by one of signals determined by the lead angle circuit 18 upon either of the first angle signal a or the second angle signal b which is determined by the output of the signal coil 8b at the engine ignition timing, charge of the capacitor 12 is supplied to the ignition coil 14 to produce a spark at the ignition plug 15.
Since the output of the ignition power generating coil 15 is supplied to a base of the transistor 10a constituting the mask means 10 through the resistor 10b, and a collector and an emitter thereof are connected to a gate of the semiconductor switching element 13 and to a grounding point, respectively, a collector-emitter circuit of the transistor 10a is on-off controlled by the output of the coil 5. That is, the transistor 10a is turned on with the positive portion of the output of the ignition power generating coil 5 to branch the ignition signal to thereby make it ineffective and is turned off with the negative portion of the output of the coil 5 to make the ignition signal effective.
FIG. 9 shows waveforms A, B, C, D and E of magnetic flux of the magnet of the conventional magnetogenerator, an output voltage generated by the ignition power generating coil 5, voltage generated in the signal coil 8b, voltage generated by the coil 5 when the engine rotation is reversed, and voltage generated in the signal coil 8b when the engine rotation is reversed, respectively. As is clear from these waveforms, when the engine is rotating in a normal direction, the transistor 10a is cut-off with the negative portion of the output of the coil 5 and the effective ignition signal is supplied to the gate of the semiconductor switching element 13. On the other hand, since, during the reverse rotation of engine, the ignition signal is produced while the output of the coil 5 is positive on which the transistor 10a is turned on, the ignition signal from the coil 8b is ineffective and thus no ignition occurs, and as a result, a continuous reverse rotation of the engine is prevented.
However, in the CDI using the magnetogenerator having 12 magnets of a common length, a half cycle of the output of the coil 5 corresponds to 30.degree. and, therefore, the ignition signal has to be generated within this angle. Thus, the lead angle of ignition timing must be limited not more than 30.degree..